Asequence is defined by the recursive formula f (n + 1) = f(n) – 2. if f(1) = 18, what is f(5)?

For this case we have the following recursive formula:
 
 What we must do in this case is to evaluate different values of n until we find f (5)
 We have then:
 For n = 1:
 
 For n = 2:
 
 For n = 3:
 
 For n = 4:
 
 
 The value of the recursive formula for f (5) is given by:
 

I’m not gonna do that